The present invention relates to a sprocket assembly which, when mounted on a film projector or other film handling device, permits the ready conversion of the device to run film having various numbers of perforations per image frame, as the occasion requires.
Conventional 35 mm film projectors and cameras pull down four-perf film. "Four-perf" film signifies that each image frame which carries the visual image corresponds to four perforations along the two side edges of the film. The perforations are all spaced apart the same distance, known as the pitch length. The "pulldown" operation in either production or projection of films involves engaging the perforations on the sides of each image frame with a claw gear and bringing the frames, in sequence, into register with the appropriate apertures for exposure or projection. Four-perf pulldown means simply that to place each image frame in front of the appropriate aperture at the proper time, the four perforations along the sides of each frame are engaged and pulled down together. Currently, longtime worldwide use and acceptance of four-perf pulldown has led to its being the standard format for both production and projection of films.
Historical accident is largely responsible for the advent and current widespread use of four-perf film. The standard film gauge of 35 mm was first introduced by Thomas Edison in 1891 for use in a peep show viewing apparatus developed by his assistant, W. K. L. Dickson. Edison also chose a four-perf, 4:3 ratio frame format, where the visual frame-width to frame-length ratio is 4:3, because it happened to be compatible with this particular peep show viewing apparatus. At that time, Edison gave no thought, apparently, to the format's ever being used in the projection of motion pictures. As it turned out, this 4:3, four-perf frame format was recognized as the world standard by 1907, after the Lumiere brothers of Lyon, France, builders of the first commercially successful projectors, followed Edison's lead by accepting that format for the European film industry.
In early films, the so-called "full aperture" frame format was used. The full aperture format had a 4:3 ratio of frame width to frame length (the length being measured along the longitudinal extent of the film), otherwise known as the 1:33 aspect ratio, and resulted in nearly the entire length of film being exposed or utilized, since there was very little unexposed film between image frames. Thus, each image frame corresponds to nearly four perforations, and the slight gap between image frames filled out the space to the fourth perforation. As a result, one image frame appeared for each group of four perforations. With the addition of sound during the 1920's, the image size on the film had to be reduced to allow room for the sound track to be printed adjacent to one row of perfs, in order to continue to use the four-perf per frame film standard. In order to accommodate the sound track, the image size was reduced in both width and length, maintaining the 4:3 or 1.33 aspect ratio, so that a greater amount of unused or unexposed film was left between image frames. The reduced size, 4:3 ratio frame format is known as the "academy aperture."
To achieve a wider projected image, and thus more closely resemble a theatrical stage, the 4:3 frame format was changed to accommodate projection on a flat, wide screen. In North America, the image size was reduced from the academy aperture and conformed into a 5.5:3 ratio, popularly known as the 1.85 aspect ratio. In Europe, the flat, wide screen frame format was conformed into a 1.66 aspect ratio, which again resulted in an image size smaller than that obtained with the academy aperture. To achieve either the 1.85 or 1.66 wide, flat screen format in a theater from a 35 mm film, two techniques are presently employed: (i) a mask is placed in the projector gate, or (ii) a "hard matte" is used in the camera. In both cases, the 35 mm camera advances the film four perfs at a time, each four perfs corresponding to one image frame. The mask in the projector gate is employed when a camera is used for filming which is adapted to produce an image on the film having a 1.33 aspect ratio, since it is necessary to restrict the height of the 1.33 frame when projecting onto a screen requiring a 1.85 or 1.66 frame. The mask in the projector gate cuts off the unnecessary top and bottom portions of the 1.33 image so that it will fit the 1.85 or 1.66 image format. On the other hand, the "hard matte," which is also a type of mask, in the camera is used to record a photographic image which has the correct wide screen ratio. The mask in the camera results in a wide, unexposed portion of film between each frame and the adjacent frames.
With either of the above two techniques for obtaining the correct 1.85 or 1.66 aspect ratio image, the amount of film used is of the order of one-third greater than the combined length of the photographic images and the required spacing between images, assuming, again, that 4-perf pulldown is employed. In other words, about 25% of each film is presently not being used, and thus only 75% of the length of film carries the visual image. This excess film results in unnecessary expense for buying, processing, editing, and printing of the film used for motion pictures, as well as extra expense for storage, shipping, handling, and the like.
Another wide-screen film technique known as Cinemascope was introduced in the early 1950's. Cinemascope achieved a 2.35 aspect ratio through the use of anamorphic lenses, which squeezed the image into the 4:3 academy aperture frame in production, and subsequently unsqueezed it in projection onto a wide, curved screen. Normally a 4-perf pulldown 35 mm camera with a 2:1 anamorphic optical system would be used in filming. This system reduces the horizontal component of the scene which is recorded on the film. The projector uses a complementary 2:1 anamorphic optical system such that the horizontal component of the image is increased to conform the proportions of the projected image to those of the scene filmed. Presently, the flat, wide screen format is more popular and widely used than the anamorphic 2.35 format.
For the last fifteen years or so, there have been proposals in the film industry to convert from 4-perf production, which is now the industry standard, to other perf to image frame ratio production in order to eliminate the 25% of each film which is wasted, as referred to above. In other words, if the perforation spacing or pitch length were to remain the same, which it must for all practical purposes, a film using fewer perf pulldown, having fewer perfs corresponding to an image, is shorter than it would be using 4-perf pulldown, which has 4 perfs per frame, because less space is wasted between individual visual frames. One such proposal is found in U.S. Pat. No. 3,865,738, issued Feb. 11, 1975, to Lente. The Lente patent discloses means for producing 3-perf visual frame films for flat, wide screens or anamorphic, curved wide screens. With the recent advent of production equipment that easily converts from 4-perf to 3-perf, and with the introduction of new film stocks that will facilitate 3-perf editing, the remaining stumbling block to industry-wide conversion to 3-perf or even smaller perf films is the inability to convert cinema projectors easily and inexpensively to accept 3-perf or 4-perf release prints. Additionally, other ratios for reducing the amount of wasted film space are contemplated, including 21/2 perf per frame. It is contemplated that cinematography suppliers may introduce numerous changes in the frame to number of perforation standard in an effort to optimize picture quality and simultaneously minimize the amount of wasted, non-imaged film space between image frames.
Currently, worldwide standard projection systems use a relatively heavy feed sprocket and hold-back sprocket, a lighter-weight intermittent sprocket between the feed sprocket and hold-back sprocket, and constant-speed sprockets associated with the accompanying sound track. These sprockets are all sized and run at the appropriate speed in order to project 24 frames per second ("fps") with a 60-cycle power supply, or 25 frames per second with a 50-cycle power supply. At a 24 fps projection rate, with 4-perf films using the worldwide standard pitch length, precisely 90 feet of film are run per minute.
If other perforation to visual frame ratio films were to be produced and made available to cinema houses, modifications would have to be made to the projectors in order to project those films. The object with these other perforation to visual frame ratio films will be to project at a rate of 24 fps, and since the sprocket shafts on the conventional projectors do not change their rates of rotation, changes in sprocket sizes would be necessary in order to effect the proper film running rate. By decreasing the number of perfs per visual frame, both the amount of wasted space between visual frames, and the overall length of film needed per time unit of filming or projecting, are reduced.
For example, in order to project 24 fps of 3-perf film, precisely 67.5 feet of film would have to be run per minute. One way to effect the 67.5 feet-per-minute running rate required for 3-perf film projection would be to replace the sprockets used for 4-perf films with sprockets having only 75% of the diameter of the larger 4-perf sprockets, with the pitch length remaining the same. In one conventional projection system for 35 mm, 4-perf films, the 4-perf sprockets have 16 teeth around their circumferential peripheries on each end. Because the teeth on the projector sprockets must always have the same pitch length no matter whether 4-perf or 3-perf film is being projected, the 3-perf sprockets for this conventional system, being sized at 75% of the diameter (and, thus, the circumference as well) of the larger 4-perf sprockets, would have only 12 teeth around their circumferential peripheries at each end. Conversion of projectors involving removal of the 16-tooth sprockets (or any larger sprocket) and replacement with smaller 12-tooth sprockets (or any smaller sprocket), is a time-consuming, relatively expensive process, however, and after conversion to the smaller 3-perf sprockets the projection equipment could not be used to run 4-perf films. Conversion from 4-perf to 3-perf pulldown, and back again, depending on whether the film to be shown is 4-perf or 3-perf, is cumbersome, slow, expensive, and would simply not be feasible with existing equipment. This would be even more cumbersome where multiple perforation to frame standards are used in the industry, such as 21/2 perfs per frame, or other ratios. See, e.g. "Study Group on 30 Frame Film Rates," International Photographer, December, 1988, at p. 20.
One adapter system which allows use of different perf films on a single projector is disclosed in U.S. Pat. No. 4,900,293, McLendon, the disclosure of which is fully incorporated herein by reference.
Another significant savings with use of 3-perf film is potentially available in conversion of film to video. Video is run at a scanning rate of 30 fields per second, not at the presently used film rate of 24 frames per second. Video which is produced from film must be specially processed to correct for these differences in rate. A desirable alternative to such special processing would appear to be to produce and project films at 30 fps. Production of videos from 30 fps films would not involve such special processing. Such an increase in film production and projection rates would, however, increase the amount of film used in a motion picture by 25%. With 3-perf film, even with an increase in production and projection rates to 30 fps to be compatible with video, film usage would still be less than with 4-perf film running at the standard 24 fps. Three-perf film running at 30 fps uses 84.375 feet of film per minute. compared with 90 feet per minute for 4-perf film running at 24 fps. These same relative film savings of about 6% will accrue whether one is using 3-perf film to produce standard video or High Definition TV. The latter is expected to become increasingly popular. Additional savings can be anticipated if lower perf to video frame ratios become popular, such as 21/2 perfs per frame.
The conversion sprocket disclosed in U.S. Pat. No. 4,900,293, McLendon, employs a two sprocket system having a 12 tooth first sprocket which connects directly to the projector shaft for showing 3-perf film and a second 16-tooth sprocket which mounts on the 12 tooth sprocket for showing 4-perf film. A set screw may be used to attach the 12-tooth sprocket to the projector shaft, and a second set screw is used to lock the 12-tooth sprocket to the 16 tooth sprocket. This system provides an effective reliable conversion between 3- and 4- perf film, but it does have two minor drawbacks. As shown in the patent, the inner surface of the outer, 16-tooth sprocket, has a plurality of grooves to receive the individual teeth of the 12-tooth inner sprocket. This profile for the ID of the outer sprocket involves a good deal of machining and is therefore relatively expensive to manufacture. Also, where a change inn sprockets is required, either from the 4-perf to the 3-perf or vice versa, the second set screw must be tightened or loosened, as the case may be. In addition to the time required for the operator to perform this task, the operator must keep an allen wrench (or the like) with him, or with the equipment, for actuating the set screw.
Thus, it will be appreciated that it would be advantageous to provide a releasable interlocking means for the inner and outer sprockets which is cheaper to manufacture than the device disclosed in the '293 patent, but just as effective, and it would also be advantageous to eliminate the need for using hand tools to effect a sprocket change.